Abstract
In flowering plants, development of the haploid male gametophytes (pollen grains) takes place in a specialized structure called the anther. Successful pollen development, and thus reproduction, requires high secretory activity in both anther tissues and pollen. In this paper, we describe a novel member of the eukaryotic type V subfamily (P(5)) of P-type ATPase cation pumps, the MALE GAMETOGENESIS IMPAIRED ANTHERS (MIA) gene. MIA protein is highly abundant in the endoplasmic reticulum and small vesicles of developing pollen grains and tapetum cells. T-DNA insertional mutants of MIA suffer from imbalances in cation homeostasis and exhibit a severe reduction in fertility. Mutant microspores fail to separate from tetrads and pollen grains are fragile with an abnormal morphology and altered cell wall structure. Disruption of MIA affects expression of genes essential for secretion as well as a high number of genes encoding cell wall proteins and membrane transporters. MIA functionally complements a mutant in the P(5) ATPase homolog SPF1 from Saccharomyces cerevisiae, suggesting a common function for P(5) ATPases in single and multicellular organisms. Our results suggest that MIA is required in the secretory pathway for proper secretion of vesicle cargo to the plasma membrane.